As wireless communication technologies have rapidly advanced in recent years, communication systems have undergone drastic changes. Currently, the LTE system is in the spotlight as a fourth generation (4G) mobile communication technology. The LTE system supports not only basic handover between different cells (which have been supported by earlier generation communication technologies) but also extended types of handover according to various scenarios.
Handover (or handoff) refers to the process of transferring the user's connection from one base station to another base station while maintaining ongoing call and data sessions. That is, handover may occur when a user equipment (UE) receiving a call service moves from the cell boundary of the current base station to the cell boundary of a neighboring base station. The base station providing a communication channel to the UE before handover may be referred to as a source cell or source base station, and the base station providing a communication channel to the UE after handover may be referred to as a target cell or target base station. That is, the UE communicates through the source cell before handover and communicates through the target cell after handover.
In an existing communication system, when a handover event occurs as to a UE, the source base station forwards data for the UE to the target base station, and the target base station transmits the forwarded data to the UE after the UE is connected to the target base station. In such a situation, it takes time to transmit, receive and interpret messages until the data forwarded to the target base station is transmitted to the UE. This may degrade user convenience. Hence, it is necessary to reduce the time required to transmit the forwarded data.